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THE ESTIMATION OF THE HUMUS ACIDS STRUCTURAL AND COMPOSITION IN THE SOILS OF THE EURO-ARCTIC ZONE AND THEIR ECOPROTECTIVE ROLE TO TRACE METALS

Natal'ya S. Prilutskaya

Abstract

The humus acids, which are part of organic matter, are an important part of the soil. Their properties affect the various pollutants, including trace metals. The article presents the structural and functional composition of humuc acids in the Euro-Arctic zone soils, which was investigated by the methods of molecular spectroscopy. An assessment of ecoprotective role to trace metals was made, which especially important for sensitive Arctic soils, formed under the influence of permafrost (cryogenic) processes. Different types of soils of the Euro-Arctic region were chosen as the object of study: gleyish easy loamy pelosi on loamy moraine (Kanin peninsula, cape Kanin Nos); humus-peat oligotrophic soil (Kolguev Island, Bugrino village); typical non-calcic loamy gley soil (Vaigach Island); gray humous iron sandy lithozem (Franz Josef Land Archipelago, Heiss Island). To study the structural and functional composition humus acids was extracted from the soil with an alkaline solution of sodium pyrophosphate. Humic, fulvic and hymatomelanic acids were isolated with appropriate solvents. Additional extraction of fulvic acidswas made by adsorption chromatography with activated carbon as a sorbent. Methylene (?CH2), carboxyl (?COOH), alcohol ?OH, thiocarbonyl (?C = S), amine (?NH2), and amide (?CONH2) groups were identified by IR spectroscopy in these acids. Based on the qualitative analysis of the IR spectra, it has been suggested that humic and hymatomelanic acids will have the maximum complexing properties to trace metals. From the calculation of the optical densities ratios certain absorption bands, a quantitative assessment of the functional composition of humus acids. The optical densities ratios of absorption lines showed a quantitative estimate of the humus acids functional composition. An increase in the relative size of molecules and, consequently, an increase in their ecoprotective role to trace metals in the series: fulvic acid > humic acid > hymatomelanic acids was established. This is explained by more branched aliphatic chains and the presence of significant amounts of carbohydrate components. It has been shown that humus acids isolated from the typical non-calcic loamy gley soil (Vaigach Island) will perform the barrier function to a greater degree. The analyzed soils according to the degree of the barrier functions of humus acids can be arranged in a series: typical non-calcic loamy gley soil > humus-peat oligotrophic soil> gray humous iron sandy lithozem > gleyish easy loamy pelosi on loamy moraine. A qualitative analysis of the UV / visible spectra, which was recorded using 0.005% alkaline solutions (0.1N NaOH), suggested that humic and hymatomelanic acids of peat oligotrophic soil contain more developed peripheral aliphatic component. These acids will bind heavy metals more strongly, and their ecoprotective role will be more active. Humus acids of other types of soil have a more developed aromatic component. The quantitative evaluation of humus acids was carried out using such parameters as: aromaticity, using the Pieravuori formula, extinction coefficient E 0.005%1cm, 465, adsorption ratio D400/D600, characterizing the degree of humification, and adsorption ratio D465/D650, characterizing the degree of the aromatic core condensation and presence of conjugate fragments. A quantitative analysis of the UV / visible spectra confirmed that humi? and hymatomelanic acids of humus-peat oligotrophic soil have a maximum barrier mechanism for trace metals, due to the high content of phenolic and carboxyl groups in the acids, the highest degree of oxidation and a more developed chain conjugated bonds. But it has been established that in all types of soils, the process of humus formation proceeds mainly to the degradation type - in the direction of the fulvic acids formation.

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DOI resolver: doi.org/10.5593/sgem2019/3.2/s13.061

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